The genus Bordetella includes important human and animal respiratory pathogens. Despite its extensive use since the 1940s, the Bordetella pertussis vaccine has substantial problems; it provides incomplete protection from disease and has no effect on the infection rate, allowing bacteria to circulate on an ongoing basis. Although it is clear that this intramuscular vaccine does not generate the same protection as infection of the respiratory mucosa, lack of understanding of the mechanisms of protective immunity hampers its improvement. In the mouse model, B cells are required to clear infection but adoptive transfer of immune serum had little effect on bacterial numbers, interpreted to mean B cells perform some function other than antibody production. We propose an alternative interpretation; secretory antibodies are the primary mechanism of protective immunity to B. pertussis. This would explain the requirement for B cells and the lack of effect of transfer of immune serum, which contains little IgA. It also suggests that vaccines prevent severe disease via serum antibody-mediated neutralization of toxins, but do not affect bacterial colonization levels because they do not induce secretory IgA within the respiratory tract. We have recently observed that, unlike B. pertussis, serum antibodies are sufficient to clear B. bronchiseptica from the lower respiratory tract of mice. The extraordinarily close phylogenetic relatedness and the genomic sequences of these two subspecies will allow both similarities and differences to be both related to the diseases they cause and interpreted in light of their comparative genomics and the recent emergence of the human pathogen. In this proposal we will determine the roles of antibodies, and their mechanisms of action, in control and clearance of Bordetella subspecies. Aim 1. We will use mice lacking B cells and adoptive transfer of antibodies, and specific isotypes, to determine the role of antibodies in bacterial control/clearance. Aim 2. Mice lacking specific antibody effector functions will be used to determine the contribution of each to the antibody effects. Preliminary results indicate these effects, and the mechanisms involved, differ in various respiratory organs and with different Bordetella subspecies. Aim 3. We have determined that adoptively transferred antibodies have very different effects than do those endogenously produced in response to infection, paralleling observations of vaccine-induced, as opposed to infection-induced, immunity. We will compare adoptively transferred and naturally produced antibodies using wild type, B cell deficient or IgA-deficient mice to understand the basis for these differences. These experiments will characterize the interactions of Bordetella subspecies with host antibodies to determine the mechanisms of antibody-mediated bacterial clearance from the respiratory tract. Similar mechanisms are likely to be involved in respiratory immunity to other organisms, including those considered potential bioterrorism threats.